U.S. patent application number 12/642269 was filed with the patent office on 2010-06-24 for current perpendicular to plane (cpp) magnetic read head.
Invention is credited to Katsumi Hoshino, Katsuya Mitsuoka, Koichi Nishioka, Koji Sakamoto, Yo Sato.
Application Number | 20100157465 12/642269 |
Document ID | / |
Family ID | 42265684 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100157465 |
Kind Code |
A1 |
Sakamoto; Koji ; et
al. |
June 24, 2010 |
CURRENT PERPENDICULAR TO PLANE (CPP) MAGNETIC READ HEAD
Abstract
One general embodiment of the present invention is a magnetic
read head including a magnetoresistive sensor where sense current
flows in a stacking direction of the magnetoresistive sensor, i.e.,
perpendicular to the plane of the layers of the head. The
magnetoresistive sensor comprises a free layer having a
magnetization direction that is affected by external magnetic
fields and includes a Heusler alloy layer and a Co-based amorphous
metal layer, a fixed layer which is stacked with the free layer and
has a fixed magnetization direction, and a non-magnetic
intermediate layer between the free layer and the fixed layer.
Inventors: |
Sakamoto; Koji;
(Kanagawa-ken, JP) ; Nishioka; Koichi;
(Kanagawa-ken, JP) ; Mitsuoka; Katsuya;
(Kanagawa-ken, JP) ; Hoshino; Katsumi; (Kanagawa,
JP) ; Sato; Yo; (Kanagawa, JP) |
Correspondence
Address: |
ZILKA-KOTAB, PC- HIT
P.O. BOX 721120
SAN JOSE
CA
95172-1120
US
|
Family ID: |
42265684 |
Appl. No.: |
12/642269 |
Filed: |
December 18, 2009 |
Current U.S.
Class: |
360/75 ; 360/319;
G9B/21.003 |
Current CPC
Class: |
G11B 5/3906 20130101;
G11B 2005/3996 20130101; H01F 10/3272 20130101; H01F 10/3295
20130101; B82Y 25/00 20130101; H01F 10/16 20130101; H01F 10/3281
20130101; B82Y 10/00 20130101; H01F 10/1936 20130101; G11B 5/3929
20130101; G01R 33/098 20130101 |
Class at
Publication: |
360/75 ; 360/319;
G9B/21.003 |
International
Class: |
G11B 21/02 20060101
G11B021/02; G11B 5/33 20060101 G11B005/33 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2008 |
JP |
2008-323473 |
Claims
1. A magnetic read head including a magnetoresistive sensor where
sense current flows in a stacking direction of the magnetoresistive
sensor, the magnetoresistive sensor comprising: a free layer having
a magnetization direction that is affected by external magnetic
fields and including a Heusler alloy layer and a Co-based amorphous
metal layer; a fixed layer which is stacked with the free layer and
has a fixed magnetization direction; and a non-magnetic
intermediate layer between the free layer and the fixed layer.
2. The magnetic read head according to claim 1, wherein the
Co-based amorphous metal layer includes at least one element
selected from a group consisting of Ta, Ti, Zr, Nb, Hf, W and
B.
3. The magnetic read head according to claim 1, wherein the free
layer further includes a metal crystal soft magnetic layer, and the
Co-based amorphous metal layer is provided between the soft
magnetic layer and the Heusler alloy layer.
4. The magnetic read head according to claim 3, wherein the
Co-based amorphous metal layer is made of Co--Fe--X, where X is one
or more elements selected from a group consisting of Ta, Ti, Zr,
Nb, Hf, W and B.
5. The magnetic read head according to claim 4, wherein the
Co-based amorphous metal layer is one or more orders of magnitude
thinner than the Heusler alloy layer.
6. The magnetic read head according to claim 3, wherein the order
of magnitude of the thickness of the Co-based amorphous metal layer
is no less than the order of magnitude of thickness of the Heusler
alloy layer.
7. The magnetic read head according to claim 1, wherein the
Co-based amorphous metal layer is made of Co--X, where X is one or
more elements selected from a group consisting of Ta, Ti, Zr, Nb,
Hf, W and B.
8. The magnetic read head according to claim 1, wherein the fixed
layer includes a Heusler alloy layer.
9. The magnetic read head according to claim 1, wherein the free
layer further includes a nanomagnetic layer having a BCC structure,
and wherein the non-magnetic intermediate layer, the nanomagnetic
layer and the Heusler alloy layer are formed successively in this
order, and the nanomagnetic layer is one or more orders of
magnitude thinner than the Heusler alloy layer.
10. The magnetic read head according to claim 9, wherein the
nanomagnetic layer is made of a Co--Fe alloy and the Fe proportion
is 30 at % or more.
11. A system, comprising: a magnetic recording medium; at least one
magnetic head as recited in claim 1; a drive mechanism for passing
the magnetic recording medium over the magnetic head; and a
controller coupled to the magnetic head for controlling operation
of the magnetic head.
12. A magnetic read head including a magnetoresistive sensor where
sense current flows in a stacking direction of the magnetoresistive
sensor, the magnetoresistive sensor comprising: a free layer having
a magnetization direction that is affected by external magnetic
fields and including a Heusler alloy layer and a Co-based amorphous
metal layer, wherein the Co-based amorphous metal layer includes at
least one element selected from a group consisting of Ta, Ti, Zr,
Nb, Hf, W and B; a fixed layer which is stacked with the free layer
and has a fixed magnetization direction; and a non-magnetic
intermediate layer between the free layer and the fixed layer.
13. The magnetic read head according to claim 12, wherein the free
layer further includes a metal crystal soft magnetic layer, and the
Co-based amorphous metal layer is provided between the soft
magnetic layer and the Heusler alloy layer.
14. The magnetic read head according to claim 13, wherein the
Co-based amorphous metal layer is made of Co--Fe--X, where X is one
or more elements selected from a group consisting of Ta, Ti, Zr,
Nb, Hf, W and B.
15. The magnetic read head according to claim 14, wherein the
Co-based amorphous metal layer is one or more orders of magnitude
thinner than the Heusler alloy layer.
16. The magnetic read head according to claim 13, wherein the order
of magnitude of the thickness of the Co-based amorphous metal layer
is no less than the order of magnitude of thickness of the Heusler
alloy layer.
17. The magnetic read head according to claim 12, wherein the
Co-based amorphous metal layer is made of Co--X, where X is one or
more elements selected from a group consisting of Ta, Ti, Zr, Nb,
Hf, W and B.
18. The magnetic read head according to claim 12, wherein the fixed
layer includes a Heusler alloy layer.
19. The magnetic read head according to claim 12, wherein the free
layer further includes a nanomagnetic layer having a BCC structure,
and wherein the non-magnetic intermediate layer, the nanomagnetic
layer and the Heusler alloy layer are formed successively in this
order, and the nanomagnetic layer is one or more orders of
magnitude thinner than the Heusler alloy layer.
20. The magnetic read head according to claim 19, wherein the
nanomagnetic layer is made of a Co--Fe alloy and the Fe proportion
is 30 at % or more.
21. A system, comprising: a magnetic recording medium; at least one
magnetic head as recited in claim 12; a drive mechanism for passing
the magnetic recording medium over the magnetic head; and a
controller coupled to the magnetic head for controlling operation
of the magnetic head.
Description
RELATED APPLICATIONS
[0001] The present application claims priority to a Japanese Patent
Application filed Dec. 19, 2008, under Appl. No. 2008-323473, which
is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to the structure of a current
perpendicular to plane (CPP) magnetic read head, in particular, to
the structure of a free layer in a CPP magnetic read head.
BACKGROUND OF THE INVENTION
[0003] A hard disk drive (HDD) is typically equipped with a
magnetic recording medium and a magnetic head, and the magnetic
head reads and writes data on the magnetic recording medium. The
magnetic head in the HDD typically includes a write head for
writing information on the magnetic recording medium (magnetic
disk) as magnetic signals and a read head for reading out signals
recorded on the magnetic recording medium as magnetic signals. The
read head typically includes a magnetoresistive effect laminated
body having a plurality of magnetic thin films and non-magnetic
thin films and it is called a magnetoresistive effect head because
it reads signals by utilizing the magnetoresistive effect.
[0004] There are several kinds of laminated structures for
magnetoresistive effect heads and they are classified into
categories such as an AN MR head, a GMR head, a CPP-GMR head, and a
TMR head in accordance with the principle of the magnetic
resistance used therein. They use magnetoresistive effect (AN MR),
giant magnetoresistive effect (GMR), current perpendicular to plane
GMR effect (CPP-GMR effect), tunnel magetoresistive effect (TMR),
respectively, and transduce input magnetic fields entering the read
head from the magnetic recording medium into voltage
variations.
[0005] Nowadays, development in high recording density has created
a requirement for a reading scheme with higher sensitivity. In a
range of 500 (Gb/in..sup.2) to 2 (Tb/in..sup.2), the TMR which has
a very high MR ratio is advantageous in view of an improvement of
sensitivity. For ultra high recording density exceeding 2
(Tb/in..sup.2), the CPP-GMR or the like is expected to be the main
type used. Being different from the current in plane GMR (CIP-GMR)
in which the sense current flows parallel to the film planes of the
magnetoresistive effect stacked body, the TMR and the CPP-GMR are
schemes in which the sense current flows perpendicular to the film
planes, i.e., in the direction of stacking of the film planes. In
the present specification, the scheme like this is referred to as a
CPP scheme; and a read head using a CPP scheme is referred to as a
CPP read head.
[0006] The magnetoresistive effect laminated body typically
includes a fixed layer whose magnetization direction is fixed and a
free layer whose magnetization direction changes with external
magnetic fields. The magnetoresistance change and output increase
with the spin polarizability of the free layer. One type of
half-metals with a 100% or almost 100% spin polarizability is
Heusler alloy. It is proposed to use a Heusler alloy in a free
layer in Japanese Unexamined Patent Application Publication No.
2008-227457.
[0007] If a Heusler alloy is used in a free layer, however, the
magnetostriction is so large that the element easily becomes
unstable. Thus, Japanese Unexamined Patent Application Publication
No. 2008-227457 proposes a free layer structure with a Heusler
alloy layer, a soft magnetic layer and a magnetostriction reduction
layer between them. The magnetostriction reduction layer consists
of elements of the fourth group, the fifth group or the sixth
group. It indicates that the free layer structure achieves a high
MR ratio and low magnetostriction.
[0008] Japanese Unexamined Patent Application Publication No.
2008-227457 discloses a magnetostriction reduction layer made of a
Hf film, a Ti film, a Zr film, a Ta film or a W film. If an
intermediate layer is formed between a Heusler alloy layer and a
soft magnetic layer, however, it is important to consider the
magnetic coupling between the Heusler alloy layer and the soft
magnetic layer.
[0009] If the intermediate layer between the Heusler alloy layer
and the soft magnetic layer is made of a non-magnetic material like
the material disclosed in Japanese Unexamined Patent Application
Publication No. 2008-227457, the magnetic coupling of the Heusler
alloy layer and the soft magnetic layer is severed, so they do not
work integrally but work independently. Thus, the magnetic volume
of each of the layers is reduced compared to the layers working
integrally, resulting in the increase of magnetic fluctuations
caused by thermal excitation. The fluctuations increase noise in
read operations of the read head and error rates. Thus, it is
preferable that the intermediate layer has a property such that the
Heusler alloy layer and the soft magnetic layer work integrally.
Namely, non-magnetic materials are not preferred for the
intermediate layer and it is preferably made of a magnetic
material.
[0010] Accordingly, a technique is desired to accomplish a high MR
ratio and low magnetostriction in a CPP magnetic read head with a
free layer including a Heusler alloy layer and provide a CPP read
head having a superior noise property as well.
SUMMARY OF THE INVENTION
[0011] One general embodiment of the present invention is a
magnetic read head including a magnetoresistive sensor where sense
current flows in a stacking direction of the magnetoresistive
sensor, i.e., perpendicular to the plane of the layers of the head.
The magnetoresistive sensor comprises a free layer having a
magnetization direction that is affected by external magnetic
fields and includes a Heusler alloy layer and a Co-based amorphous
metal layer, a fixed layer which is stacked with the free layer and
has a fixed magnetization direction, and a non-magnetic
intermediate layer between the free layer and the fixed layer.
[0012] Any of these embodiments may be implemented in a magnetic
data storage system such as a disk drive system, which may include
a magnetic head, a slider for supporting the head, a drive
mechanism for passing a magnetic medium (e.g., hard disk) over the
magnetic head, and a control unit electrically coupled to the
magnetic head for controlling operation of the head.
[0013] Other aspects and advantages of the present invention will
become apparent from the following detailed description, which,
when taken in conjunction with the drawings, illustrate by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view schematically showing the
structure of a magnetic head according to one embodiment.
[0015] FIG. 2 is a cross-sectional view schematically illustrating
the structure of a CPP read head according to one embodiment.
[0016] FIGS. 3(a) and 3(b) schematically illustrate the laminated
structure of a magnetoresistive sensor according to one
embodiment.
[0017] FIG. 4 schematically illustrates a preferred example of a
magnetoresistive sensor with the laminated structure depicted in
FIG. 3(a).
[0018] FIG. 5 schematically illustrates a preferred example of a
magnetoresistive sensor with the laminated structure depicted in
FIG. 3(b).
[0019] FIGS. 6(a) and 6(b) show measurement data comparing a
magnetoresistive sensor according to the present embodiment and a
magnetoresistive sensor with conventional structure.
[0020] FIG. 7 shows measurement data of MR outputs with different
relative proportions of a Heusler alloy layer.
DETAILED DESCRIPTION
[0021] The following description is made for the purpose of
illustrating the general principles of the present invention and is
not meant to limit the inventive concepts claimed herein. Further,
particular features described herein can be used in combination
with other described features in each of the various possible
combinations and permutations.
[0022] Unless otherwise specifically defined herein, all terms are
to be given their broadest possible interpretation including
meanings implied from the specification as well as meanings
understood by those skilled in the art and/or as defined in
dictionaries, treatises, etc.
[0023] it must also be noted that, as used in the specification and
the appended claims, the singular forms "a," "an" and "the" include
plural referents unless otherwise specified.
[0024] One general embodiment of the present invention is a
magnetic read head including a magnetoresistive sensor where sense
current flows in a stacking direction of the magnetoresistive
sensor, i.e., perpendicular to the plane of the layers of the head.
The magnetoresistive sensor comprises a free layer having a
magnetization direction that is affected by external magnetic
fields and includes a Heusler alloy layer and a Co-based amorphous
metal layer, a fixed layer which is stacked with the free layer and
has a fixed magnetization direction, and a non-magnetic
intermediate layer between the free layer and the fixed layer.
[0025] In a preferred configuration, the Co-based amorphous metal
layer includes at least one element selected from the following
group: Ta, Ti, Zr, Nb, Hf, W and B. In a preferred configuration,
the free layer further includes a metal crystal soft magnetic
layer, and the Co-based amorphous metal layer is provided between
the soft magnetic layer and the Heusler alloy layer. Further, the
Co-based amorphous metal layer is preferably made of Co--Fe--X,
where X is one or more elements of Ta, Ti, Zr, Nb, Hf, W and B.
Further, the Co-based amorphous metal layer may be one or more
orders of magnitude thinner than the Heusler alloy layer.
Alternatively, the order of magnitude of the thickness of the
Co-based amorphous metal layer is no less than the order of
magnitude of thickness of the Heusler alloy layer.
[0026] In a preferred configuration, the Co-based amorphous metal
layer is made of Co--X, where X is one or more elements selected
from Ta, Ti, Zr, Nb, Hf, W and B. In a preferred configuration, the
fixed layer includes a Heusler alloy layer. In a preferred
configuration, the free layer further includes a nanomagnetic layer
having a BCC structure, where the non-magnetic intermediate layer,
the nanomagnetic layer and the Heusler alloy layer are formed
successively in this order, and the nanomagnetic layer is one or
more orders of magnitude thinner than the Heusler alloy layer. In
one approach, the nanomagnetic layer is made of a Co--Fe alloy and
the Fe proportion is 30 at % or more.
[0027] Accordingly, the present invention, according to several
embodiments thereof, p[provides a CPP read head with a high MR
ratio and low magnetostriction.
[0028] Hereinafter, a preferred embodiment of the present invention
is described referring to the drawings. Throughout the drawings,
the like components are denoted by like reference numerals, and
their repetitive description is omitted if not necessary for the
sake of clearness in the explanation. In the preferred embodiment
described hereinbelow, the present invention is applied to a read
head for a hard disk drive (HDD). The read head according to the
present embodiment is a current perpendicular to plane (CPP) head
in which sense current flows in the laminating direction of the
magnetoresistive sensor film (perpendicular to the plane).
[0029] A CPP magnetic head according to one embodiment has a
feature in a free layer structure in a magnetoresistive sensor
film. A free layer according to the present embodiment includes
stacked layers and has a Heusler alloy layer and a Co-based
amorphous metal layer. The free layer structure accomplishes a high
MR ratio and low magnetostriction and provides a CPP head with a
superior noise property.
[0030] Before describing a feature of the CPP read head according
to the present embodiment, the entire configuration of the magnetic
head will be outlined. FIG. 1 is a cross-sectional view
schematically showing the structure of the magnetic head 1. The
magnetic head 1 reads and writes data from and to a magnetic disk
3. The magnetic head 1 is equipped with a read head 11 and a write
head 12 arranged in order from its traveling direction side
(leading side). The magnetic head 1 is formed on the trailing side
(the other side of the leading side) of a slider 2. The read head
11 includes a lower shield 111, a magnetoresistive sensor 112, and
an upper shield 113 in order from the leading side.
[0031] The write head 12 includes a thin film coil 121 and write
magnetic poles 122. The thin film coil 121 is enclosed with an
insulator 123. The write head 12 is an inductive element for
generating magnetic fields between the write magnetic poles 122
from electric current running through the thin film coil 121 and
for writing magnetic data onto the magnetic disk 3. The read head
11 is a magnetoresistive element and includes a magnetoresistive
sensor 112 having magnetic anisotropy and reads out magnetic data
recorded on the magnetic disk 3 by use of the resistance changing
in accordance with magnetic fields from the magnetic disk 3. The
read head according to one embodiment is a CPP read head and the
lower shield 111 and the upper shield 113 are used as electrodes
for supplying the magnetoresistive sensor 112 with detection
current.
[0032] The magnetic head 1 is formed on an AlTic substrate
constituting the slider 2 by using a thin film forming process. The
magnetic head 1 and the slider 2 constitute a head slider. The head
slider flies over the magnetic disk 3 and the surface 21 facing the
magnetic disk is called an air bearing surface (ABS). The magnetic
head 1 is equipped with a protective film 13 made of alumina, for
example, around the write head 12 and the read head 11, and the
entire magnetic head 1 is protected by the protective film 13.
[0033] FIG. 2 is a cross-sectional view schematically illustrating
the structure and configuration of the CPP read head 11 in which
the magnetoresistive sensor structures described herein may be
employed. FIG. 2 schematically depicts its cross-sectional
structure as viewed from the ABS 21 of the head slider. The bottom
of FIG. 2 is the leading side and the top is the trailing side. In
the present specification, the AlTic substrate side on which the
read head 11 is formed, i.e., the slider 2 side, is defined as the
bottom and the opposite trailing side is defined as the top. The
each layer of the read head 11 may be formed sequentially from the
bottom. The read head II of the present embodiment is a current
perpendicular to plane magnetoresistance (CPP-MR) head and sense
current flows in the layer stack direction (vertical to the film
plane and up-down direction in FIG. 2).
[0034] The magnetoresistive sensor 112 is a multi-layer film having
a plurality of layers. The magnetoresistive sensor 112 is provided
between the lower shield 111 and the upper shield 113. The lower
shield 111 and the upper shield 113 function as magnetic shields,
and a lower electrode and an upper electrode respectively for
supplying sense current to the magnetoresistive sensor 112. Under
the upper shield 113, an upper magnetic separation film 114 made of
an electrical conductor is formed.
[0035] The magnetoresistive sensor 112 comprises a sensor
underlayer 211, an antiferromagnetic film 212, a fixed layer 213, a
non-magnetic intermediate layer 214, a free layer 215, and a sensor
cap film 216 sequentially stacked from the lower layer. Each layer
preferably physically contacts the adjacent layers. The sensor
underlayer 211 is made of non-magnetic material such as Ta and a
NiFeCo alloy, and may be a single layer structure as shown in the
drawing or a laminated structure.
[0036] Exchange interaction with the anti-ferromagnetic film 212
works on the fixed layer 213 so that the magnetization direction is
fixed. The track width of the free layer 215 is denoted by Twf. The
magnetoresistive effect head, in use, utilizes the resistance
changes caused by changes in the magnetization direction of the
free layer 215 relative to the magnetization direction of the fixed
layer 212. Namely, if the magnetization direction of the free layer
215 relative to the magnetization direction of the fixed layer 213
changes due to magnetic fields from the magnetic disk, the
resistance (current value) of the magnetoresistive sensor 112
changes. Thereby, the read head 11 or system can detect narrowed
external information magnetic fields by detecting the resistance
(current value) of the magnetoresistive sensor 112.
[0037] In order to suppress Barkhausen noise caused by non-uniform
magnetic domains of the free layer 215, hard bias films 115 which
are magnetic domain control films may be provided at the right and
left sides of the magnetoresistive sensor 112. Typically, the hard
bias films 115 are made of a Co alloy and made of a CoCrPt alloy or
a CoPt alloy, for example. Bias magnetic fields from the hard bias
films 115 act on the free layer 215 to have a single magnetic
domain and stabilize the magnetic action of the free layer.
[0038] The hard bias films 115 are formed on the hard bias
underlayer films 116. As lower layers of the hard bias underlayer
films 116, junction insulating films 117 are formed. The junction
insulating films 117 are provided between the hard bias underlayer
films 116 and a lower shield film 111 and the magnetoresistive
sensor 112 and they cause sense current not to flow outside of the
magnetoresistive sensor 712. The junction insulating films 117 may
be made of Al.sub.2O.sub.3, for example, or any other insulating
material. The magnetoresistive sensors described herein may be
applied to a read head having a different hard bias film
structure.
[0039] FIGS. 3(a) and 3(b) schematically illustrate the laminated
structure of magnetoresistive sensor s112 according to two
embodiments. As described referring to FIG. 2, the magnetoresistive
sensor 112 has the antiferromagnetic layer 212, the fixed layer
213, the non-magnetic intermediate layer 214, the free layer 215
and the cap layer 216 sequentially stacked from the lower layer.
The stacking order of the layers except for the cap layer 216 may
be reversed. Namely, the free layer, the non-magnetic intermediate
layer, the fixed layer and the antiferromagnetic film may be
sequentially stacked from the lower layer.
[0040] The antiferromagnetic layer 212 is made of a
antiferromagnetic material such as PtMn and MnIr. The fixed layer
213 is typically a laminated fixed layer and includes two
ferromagnetic layers and a non-magnetic layer between them. For
example, the ferromagnetic layers are made of a CoFe alloy and the
non-magnetic layer is made of Ru. The two ferromagnetic layers are
coupled by exchange interaction and the fixed magnetization is
stabilized. The exchange interaction with the antiferromagnetic
film 212 is acted on the lower ferromagnetic layer and the
magnetization direction is fixed. The fixed layer 213 may have a
single layer structure. The non-magnetic intermediate layer 214 is
typically made of non-magnetic conductor, for example, made of Cu.
The sensor cap film 216 is made of a non-magnetic conductive
material, Ta for example.
[0041] A feature of the magnetoresistive sensor 112 disclosed
herein is that the free layer 215 has a Heusler alloy layer 511 and
a Co-based amorphous metal layer 512. In the structure in FIG.
3(a), the free layer 215 includes the Heusler alloy layer 511 and
the Co-based amorphous metal layer 512. In the structure in FIG.
3(b), the free layer 215 includes the Heusler alloy layer 511, a
soft magnetic layer of metal crystal 513 and the Co-based amorphous
metal layer 512 between them. The free layer 215 including the
Heusler alloy layer 511 and the Co-based amorphous metal layer 512
accomplishes a CPP read head with a high MR ratio and low
magnetostriction.
[0042] In the structures in FIG. 3(a) and FIG. 3(b), the free layer
215 may have a metal layer other than the depicted layers. The free
layer 215 may have a plurality of Heusler alloy layers, a plurality
of metal crystal soft magnetic layers or a plurality of Co-based
amorphous metal layers.
[0043] In the structure in FIG. 3(a), the Co-based amorphous metal
layer 512 and the Heusler alloy layer 511 are in contact with each
other and form an interface. It results in the large magnetic
coupling between the Co-based amorphous metal layer 512 and the
Heusler alloy layer 511. Alternatively, if the two layers are
strongly magnetically coupled, an intermediate layer may be
provided between the two layers. Specifically, a metal crystal soft
magnetic layer or an antiferromagnetic coupling layer may be
disposed between the Co-based amorphous metal layer 512 and the
Heusler alloy layer 511. As the metal crystal soft magnetic layer,
a layer made of ferromagnetic elements Co, Fe or Ni, or an alloy
thereof may be used. As the antiferromagnetic coupling layer, a
layer made of Cu or Ru may be used.
[0044] In the structure in FIG. 3(b), the Co-based amorphous metal
layer 512 and the Heusler alloy layer 511 are in contact with each
other and form an interface. The Co-based amorphous metal layer 512
and the metal crystal soft magnetic layer 513 are in contact with
each other and form an interface. It results in the great magnetic
coupling between the Heusler alloy layer 511 and the metal crystal
soft magnetic layer 513. Alternatively, if the Heusler alloy layer
511 and the metal crystal soft magnetic layer 513 are magnetically
coupled strongly, an intermediate layer may be provided between the
Co-based amorphous metal layer 512 and each of the two layers. As
an intermediate layer, a metal crystal soft magnetic layer or an
antiferromagnetic coupling layer may be formed, as described
referring to FIG. 3(a).
[0045] In the structure in FIG. 3(a), preferably, the order of
magnitude of the thickness of the Co-based amorphous metal layer
512 is no less than the order of magnitude of the thickness of the
Heusler alloy layer 511. In practical design, they are preferably
the same order of magnitude. For example, if the thickness of the
Heusler alloy layer 511 is the order of 10 .ANG., the thickness of
the Co-based amorphous metal layer 512 is also the order of 10
.ANG.. In this structure, the Co-based amorphous metal layer 512
contributes actively to the MR output with the Heusler alloy layer
511.
[0046] In contrast, in the free layer structure in FIG. 3(b), the
Co-based amorphous metal layer 512 aims to function as an
intermediate layer between the Heusler alloy layer 511 and the
metal crystal soft magnetic layer 513. Thus, preferably, the
Co-based amorphous metal layer 51 is one or more orders of
magnitude thinner than the Heusler alloy layer 511 and the metal
crystal soft magnetic layer 513. For example, if the Heusler alloy
layer 511 and the metal crystal soft magnetic layer 513 have a
thickness of several tens of angstroms, the Co-based amorphous
metal layer 512 may have a thickness of several angstroms or less.
This description about thickness can be applied to the metal
crystal soft magnetic layer and antiferromagnetic layer used as an
intermediate layer between the Co-based amorphous metal layer 512
and another layer.
[0047] In the structures shown in FIGS. 3(a) and 3(b), the Heusler
alloy layer 511 is formed at the non-magnetic intermediate layer
214 side and the Heusler alloy layer 511 is formed between the
Co-based amorphous metal layer 512 and the non-magnetic
intermediate layer 214. In order to increase the MR output by the
Heusler alloy layer 511, it is preferable that the Heusler alloy
layer 511 be located closer to the non-magnetic intermediate layer
214 than the Co-based amorphous metal layer 512. In order to obtain
a high MR output by the Heusler alloy layer 511, it is preferable
to form a nanomagnetic layer which has a BCC structure and a
thickness less than the Heusler alloy layer 511 by one or more
orders of magnitude before forming the Heusler alloy layer. Namely,
it is preferable to form the Heusler alloy layer after the
nanomagnetic layer. Preferably, the nanomagnetic layer is a Co--Fe
alloy layer with Fe of 30 at % or more having a BCC structure for a
higher MR ratio.
[0048] FIG. 4 depicts a preferred example of the magnetoresist
sensor 112 with the laminated structure in FIG. 3(a). The
antiferromagnetic layer 212 is made of Mn.sub.22Ir. The fixed layer
213 has a first fixed layer 311 of the upper layer and a second
fixed layer 312 of the lower layer and they are made of CoMnGe, a
Heusler alloy, and CO.sub.25Fe, respectively. A Ru layer, an
antiferromagnetic layer, is provided between the two fixed layers
311, 312. The fixed layer 213 preferably has a Heusler alloy layer.
It accomplishes a high MR ratio. Typically, a Heusler alloy layer
in the fixed layer 213 has the same composition as a Heusler alloy
layer in the free layer 215. The non-magnetic intermediate layer
214 includes an upper Cu layer and a lower Cu layer and an
Al.sub.10Cu layer between them. The cap layer 216 includes a Cu
layer and a Ru layer.
[0049] In the free layer 215, the Heusler alloy layer 511 is a
CoMnGe layer. Other Heusler alloys having various structures are
known. It is preferable to use a Heusler alloy having the L21
structure, X.sub.2YZ, or the B12 structure. Co may be used as X.
Mn, Cr or Fe may be used as Y. Ge, Al or Si may be used as Z.
Particularly, CO.sub.2MnGe is a preferable Heusler alloy since it
is easy to produce. It is noted that the representation of CoMnGe
does not limit the relative proportions and the present invention
can use Heusler alloys other than CoMnGe.
[0050] FIG. 7 shows measurement data of the relationship between MR
outputs and the relative proportions of a Heusler alloy layer. The
relative proportions of a Heusler alloy layer are changed by
changing the proportions of Ge and CO.sub.2Mn. The proportion of Ge
is indicated. Not only typical relative proportions of CO.sub.2MnGe
but also a wide range of relative proportion of Ge of 23 to 35 at %
can accomplish a superior MR property. Ge 30 at % is preferable in
the range since it accomplishes the highest MR output.
[0051] The Co-based amorphous metal layer 512 is a layer of Co--X:
Ta, Ti, Zr, Nb, Hf, W and B or Co--Fe--X: Ta, Ti, Zr, Nb, Hf, W and
B. Co--X and Co--Fe--X include one or more elements of the above
mentioned elements. The relative proportions of Co, Fe, and X are
not limited. Preferably, the proportion of X is 12 at % to 25 at %.
If the proportion of X is less 12 at %, the Co-based amorphous
metal layer crystallizes, so it is not preferable. If the
proportion of X is more 25 at %, the Co-based amorphous metal layer
becomes non-magnetic, so it is not preferable. The representation
of Co--X and Co--Fe--X does not restrict the relative proportions
of the constituents. These materials are preferable for the
Co-based amorphous metal layer 512 in order to accomplish a high MR
ratio and low magnetostriction.
[0052] An examples of the thicknesses of layers in the laminated
structure illustrated in FIG. 4 is from the bottom, the Mn.sub.22Ir
layer of 60 .ANG., the CO.sub.25Fe layer of 20 .ANG., the Ru layer
of 4.5 .ANG., the CoMnGe layer of 25 .ANG., the Cu layer of 5
.ANG., the Al.sub.10Cu layer of 15 .ANG., the Cu layer of 5 .ANG.,
the CoMnGe layer of 35 .ANG., the Co--X/Co--Fe--X layer of 35
.ANG., the Cu layer of 20 .ANG. and the Ru layer of 10 .ANG..
[0053] With continued reference to the structure in FIG. 4, if the
Co-based amorphous metal layer 512 has a thickness similar to the
Heusler alloy layer 511, Co--X is preferable to Co--Fe--X. This is
because Co--X has a lower magnetostriction constant than Co--Fe--X.
Co--X allows the magnetoresistive sensor 112 to exhibit the
superior low magnetostriction property even if the Co-based
amorphous metal layer 512 is thick.
[0054] FIG. 5 depicts a preferred example of the magnetoresistive
sensor 112 with the laminated structure shown in FIG. 3(b). It has
the same structure as the laminated structure depicted in FIG. 4
except for the structure of the free layer 215. In the
magnetoresistive sensor 112 in FIG. 5, the metal crystal soft
magnetic layer 513 is formed of a NiFe alloy. For the metal crystal
soft magnetic layer 513, a soft magnetic metal including any
element or any combination of elements selected from Co, Fe and Ni
may be used. The materials of the Co-based amorphous metal layer
512 and the Heusler alloy layer 511 are the same as the structure
in FIG. 4.
[0055] In the free layer 215, for example, the CoMnGe layer has a
thickness of 35 .ANG., the Co--Fe--X/Co--X layer has a thickness of
5 .ANG. and the NiFe layer has a thickness of 35 .ANG.. Even if the
Co-based amorphous metal layer 512 works as an intermediate layer,
the Co--Fe--X/Co--X layer accomplishes a high MR ratio and low
magnetostriction.
[0056] If the proportions of X in Co--Fe--X and Co--X are the same,
Co--Fe--X has a higher Curie temperature and a higher magnetic
moment per volume (magnetization). Co--X is superior to Co--Fe--X
in the magnetostriction property. Thus, in designing the
magnetoresistive sensor 112, a preferred material in the
magnetostriction property and magnetization and Curie temperature
properties is used for the Co-based amorphous metal layer 512.
[0057] Hereafter, measurement data on a magnetoresistive sensor
with a free layer structure according to the present embodiment
will be shown compared to a magnetoresistive sensor with a
conventional structure. FIG. 6(a) shows measurement data of MR
outputs and FIG. 6(b) shows measurement data of magnetostriction.
The measurement was carried out on magnetoresistive sensors with
different free layer structures and the same layer structure except
for the free layer. Specifically, the MR outputs and the
magnetostriction are measured on magnetoresistive sensors with a
free layer having a CoMnGe layer of 60 .ANG., a free layer having a
CoMnGe layer of 37 .ANG. and a NiFe layer of 37 .ANG., a free layer
having a CoMnGe layer of 32 .ANG., a CO.sub.8Fe.sub.20B layer of 5
.ANG. and NiFe of 32 .ANG., and a free layer having a CoMnGe layer
of 33 .ANG. and a CO.sub.sTa.sub.20Zr layer of 33 .ANG..
[0058] As shown in the graph of FIG. 6(a), compared to the
laminated structure having the CoMnGe layer of 37 .ANG. and the
NiFe layer of 37 .ANG., the other laminated structures exhibit high
MR ratios. In the data showing the magnetostriction in FIG. 6(b),
compared to the free layer having a single CoMnGe layer, the other
laminated structures exhibit low magnetostriction. Namely, the free
layer having the single Heusler alloy layer exhibits a high MR
ratio but the magnetostriction is also large. A free layer having a
Heusler alloy layer and a metal crystal soft magnetic layer
exhibits low magnetostriction but the low MR ratio is also
small.
[0059] In contrast, it was verified that a free layer including a
Heusler alloy layer and a Co-based amorphous metal layer had a
higher MR ratio than a free layer of a Heusler alloy layer and a
metal crystal soft magnetic layer and lower magnetostriction than a
free layer of a single Heusler alloy layer. Coexistence of a
Heusler alloy layer and a Co-based amorphous metal layer
accomplished a magnetoresistive sensor with a high MR ratio and low
magnetostriction.
[0060] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of an
embodiment of the present invention should not be limited by any of
the above-described exemplary embodiments, but should be defined
only in accordance with the following claims and their
equivalents.
* * * * *